Charge Coupled Devices (CCDs) provide a basic function of storing and moving isolated packets of electrical charge. Various operations can be performed on the charge packets. For example, multiple packets can be added together (merged), single packets may be split into two or more pieces, conditionally steered, destructively or nondestructively sensed, and the like. These operations make it possible to use CCD based circuits for various discreet time analog signal processing operations, by having signals represented as charge packets.
The present invention relates to charge splitting devices and more particularly to a Charge Coupled Device (CCD) structure in which an incoming charge packet is split into multiple outgoing charge packets.
As is known in the art, a charge coupled device (CCD) charge splitter is a CCD structure in which a single incoming charge packet is split into two or more outgoing packets. The splitting ratio, i.e., the ratio of the outgoing packets, is a design parameter of the structure.
One known type of charge splitter uses a series of storage and barrier gates. The input charge to be split is first fed to a “splitting” storage gate. The splitting gate provides a structure in which the incoming charge packet is temporarily stored and partitioned into the two or more outgoing electrical packets. Then, when the packets are allowed to spill over the outgoing barrier gate, each is collected and stored in a separate output storage gate. The ratio of the split is fixed by the geometry of the channel underneath the splitting gate. The splitting process depends upon both the initial distribution of charge under the splitting gate, and the charge outflow rate from the splitting gate to the respective output storage gates.
The splitting ratio in known types of charge splitters is fixed by the design, but is subject to variations in implementation. These variations occur for multiple reasons, but may be due to Integrated Circuit (IC) process variations (such as differences in photo masking processes, gate threshold levels, and the like) as well as operating conditions (such as supply voltage, temperature, external noise sources, and the like).